Sheril Kirshenbaum links to this graph from economists Kasey Buckles and Daniel Hungerman showing differences in who conceives babies in the fall (older, better-educated people) and the spring (younger, less well-educated people):
Pretty stunning. And a nice graph. The repeating pattern over the years is super-clear. I’d also like to see a version that just shows the averages for the 12 months, so I could see the pattern in more detail. Also I’d like to subtract 40 weeks so it shows the data by (approximate) month/date of conception.
P.S. This news article by Justin Lahart is excellent. But I did notice one funny thing (to a statistician):
The two economists examined birth-certificate data from the Centers for Disease Control and Prevention for 52 million children born between 1989 and 2001 . . . 13.2% of January births were to teen mothers, compared with 12% in May–a small but statistically significant difference, they say.
Well, yeah, with n=52,000,000, I’d think that a 1 percentage point difference would be statistically significant! More seriously, with that many cases, it sounds like the next step (if the researcher haven’t already done this) is to break things down by subgroups of the population. I wonder what data are available from the birth certificate records. To start with, there’s geographic information.